1. Field of the Invention
The present invention relates generally to a separate, external heat-dissipating device for electronic devices, more specifically, to a cooling pad for laptop-style portable computers and the like.
2. Description of the Related Art
A computer being a collection of processing units, memories, graphic processing units and various other electronic components generates substantial amounts of heat as a result of electrical and mechanical resistance from such components. As computing tasks become computation intense, more electricity is drawn and subsequently more heat generated. The introduction of solid state components into electronic devices reduced the amount of heat generated per component, but the benefits were short-lived. As the demands on silicon-based microchips and their abundance in modern computers multiplied, the amount of heat generated increased proportionally. Compounding this increase, personal computers and related electronic appliances containing processors (such will be all referred to as micro computers hereon) have continued to evolve into more lightweight and smaller-sized devices. With the reduction of the physical size of micro computers and their increasing processing power, heat dissipation becomes a major challenge for the computer manufacturers and consumers as traditional cooling methods are no longer effective.
Portable computers present a difficult problem in maintaining proper operating temperatures. Modern portable computers due to their small housing and lightweight characteristics are unable to allow for necessary convection of heat into the surrounding air. The housing of portable computers retains more heat than a normal desktop due to the small volume and reduced airflow. The rate of heat generation in portable computers outpaces the rate of heat expulsion. Furthermore in an effort to minimize noise, weight, and maintain battery life, the common use of fans and heat sinks in desktop computers are limited in portable computers. Most notebook computers accommodate these limitations, in part, by the use of low power consuming components to reduce heat generation. Many incorporate software controls to limit processing power while not in use to maintain a reasonable operating temperature. A substantial amount of heat is retained, however, and interior temperatures may reach a range dangerous to components, as well as reducing the performance and the life span of the notebook computer.
The main heat generating elements in portable computers, the circuitry and processing units, are typically packed close to the bottom-face in order to minimize the housing size. The placement makes the bottom-face a direct gateway for heat dissipation and a logical target to approach the problem of excess heat in portable computers. Although this potential is well recognized, the bottom-face of mobile computers remains the most underutilized surface for heat dissipation. Unfortunately, due to design and ergonomics, the bottom-face is unexposed much of the time to allow effective convection. Heat conduction is unreliable at the bottom-face because of surfaces in contact are usually made of poor thermal conductors, such as wooden desk or a lap. As a result, the bottom-face has universally become the hottest portion of the surface of the mobile computer housing, so hot that it often cannot be placed in contact with human skin or fine furniture. A widely-reported 2004 State University of New York study also found that laptop heat is a threat to fertility of young men, that heat increases scrotum temperatures and thereby lowers sperm counts, and through repeated exposures the damage could even be long term. An effective way to direct heat away from the bottom face of a mobile computer will not only reduce the discomfort of the computer users, but also create a healthier thermal environment around the mobile computer.
Several solutions have been developed to meet this challenge, the most popular a simple cooling fan that forces airflow over the electronic components to increase heat transfer via convection. The overall cooling effectiveness can be increased by simply increasing number of cooling fans inside of a micro computer at critical locations. Another solution is to incorporate heat sinks with heat dissipating fins directly on the electronic components to increase the cooling effectiveness of convection. The two solutions are usually applied in combination to create the satisfactory cooling result. Also known are external pads made of mere insulation material to place between the laptop and the user, exacerbating the problem of cooling the computer but offering some relief from the heat for the user's lap.
Some designs have attempted to dissipate heat through the bottom-face by supporting the notebook computer on a stand to allow forced or natural convection to take place under the notebook computer. The stands using forced convection under the notebook computer use one or more small fans to induce airflow. The small fans in the stand require power, which usually comes from the battery of the mobile computer. This method shortens the span of the mobile operation of the computer, as well as creates additional noise. The natural convection stands simply raise the notebook computer off the surface to allow easier airflow, but are very ineffective. Both present the problem of adding sizable and rigid external components to a mobile computer. Therefore, a better device for cooling the bottom face is desired.
Phase change material (PCM) is a name shared by chemical compounds that possess the physical property of changing between solid phase and liquid phase at a desirable temperature range. Examples of the PCM include compounds such as sodium sulfate decahydrate, sodium carbonate decahydrate, disodium phosphate dodecahydrate or sodium thiosulfate pentahydrate. In the process of a phase change, either melting or solidifying, the material respectively absorbs or releases a large amount of per-mass thermal energy, or “heat of fusion”. This process requires very small to no temperature or volume change of the PCM. This property can be utilized to store away excessive heat produced by a micro computer during operation when the PCM turns into liquid, and slowly release the heat when the computer is not being used when the PCM solidifies again. This process can be repeated as desired. Furthermore, this can keep the operational temperature of a micro computer at a relatively stable point. Due to the nature of such heat dissipation, however, the PCM is not suitable as a part the built-in devices of a micro computer, but it works ideally as the main component of a detached, external heat-absorbing device. Because of the fact that liquid does not take a definite form but solid material does, the nature of the phase change process in this application calls for well-designed containment both to control the PCM and to serve the purpose of heat dissipation.